(a) Field of the Invention
This invention relates to focal plane shutters and more particularly to a blade type focal plane shutter wherein, except when an exposure is made, an exposure aperture will be covered with a front blade group and rear blade group, when the shutter is released, first the rear blade group will be moved to a folded position opening the exposure aperture and then the front blade group will be moved to a folded position opening the exposure aperture to begin an exposure and, when a proper exposure time has passed, the rear blade group will be moved to an unfolded position covering the exposure aperture to end the exposure.
(b) Description of the Prior Art
Generally, in a blade type focal plane shutter, in order to reduce the cocking force or increase the moving velocities of the blades themselves at the time of an exposure, it is effective to reduce the size of each shutter blade. However, then, there will be a problem that the overlapping amount of the respective blades forming the front blade group or rear blade group in case the front blade group or rear blade group is in the unfolded position covering the exposure aperture will be so small that, as a result, the likelihood of a light leakage will increase. Therefore, there is suggested such type as is disclosed, for example, in U.S. Pat. No. 4,114,174 wherein, a rear blade group is moved to an unfolded position covering an exposure aperture to end an exposure and then a front blade group is again moved to the unfolded position covering the exposure aperture to cover the exposure aperture with the front blade group and rear blade group, this state is maintained even after the shutter is cocked and, when the shutter is released, first the rear blade group will open the exposure aperture and then the front blade group will open the exposure aperture to begin an exposure. However, such known one has defects that the mechanism is complicated and the manufacturing cost is high.